David Robson: Breaking down herbicides, insecticides and fungicides

Monday

Jun 18, 2012 at 12:01 AMJun 18, 2012 at 5:16 PM

Pesticides kill, prevent, manage or limit damage on plants and animals by pests. It’s not necessary for pesticides to kill everything; in fact, the best pesticides will keep the pest in check to the point where it’s not causing much problem.

David Robson

Some folks like perfection. A dandelion in their lawn sends them into apoplexy. Seeing a beetle causes hysterics and ear-piercing shrieks. (At least with diseases, there is more of a scratching of the chin in puzzlement.)

Others don’t care. Dandelions are viewed as something green in the lawn. Beetles may be food for some other creature. Diseases are nature’s way to get rid of the weak.

Most gardeners fall in the middle. In the past few decades, the trend is toward doing nothing compared with total eradication.

There is something to be said about perfection. Most people think golf courses look lush, and when a lawn looks the same, there is a sense of pride … or envy, depending on which side of the fence you’re standing.

Change your expectations, and you might find gardening is more fun. Realize that perfection comes with a mental and physical price: labor and the use of pesticides.

Pesticides kill, prevent, manage or limit damage on plants and animals by pests. It’s not necessary for pesticides to kill everything; in fact, the best pesticides will keep the pest in check to the point where it’s not causing much problem.

Let’s take a look at the top three: herbicides, insecticides and fungicides.

Herbicides

Herbicides are aimed at plants we’ll call weeds. Most people claim weeds are just plants out of place. What might be one person’s weed is another person’s beloved specimen. Many lawn grasses can become weedy in flower and vegetable gardens.

And some plants don’t start out as weeds. Maybe birds love their seeds, or nothing impedes the plant’s growth. Sadly, many plants the U.S. government promoted decades ago have become weeds: multiflora rose, kudzu, honeysuckles, and Russian olive. Their natural enemies were few and plants soon displaced natural specimens.

The best way to control weeds is by digging or hoeing them out. That’s acceptable for gardens and landscape beds but more difficult for lawns.

Spot treating is the next best option. If you must use a herbicide, chose a low-residual product and treat only the offending plant. Some weedkillers persist in the soil while others break down quickly.

Always read the label and determine how the weedkiller works. Some are absorbed by the roots while others are sprayed on the leaves and carried through the plant. The former could damage nearby desirable plants.

With any herbicide spray, keep drifting in mind. Most weedkillers aren’t formulated for specific plants as much as they are for specific types, such as broadleaf or grassy. Broadleaf weedkillers can do a number on tomatoes and grapes.

Of course, the more you plant, the fewer opportunities you provide for weeds to establish since there’s less space for the weeds to establish themselves.

Insecticides

Insects and related pests send some people into spasms. The thing is most insects eat other insects or organic matter, causing no major concern. Even the best gardeners accidentally kill a good guy now and then.

More plants in the landscape also limit insect damage by attracting birds and beneficial bugs. A big problem with most insecticides is most are non-selective. They kill the Japanese beetle but they also kill the scavenger Tiger beetle.

Another problem: Insects are more closely related to us than weeds or fungi. Bugs have nervous and digestive systems; many insecticides target those. That means a misapplication can affect us or our pets.

That’s not saying you shouldn’t use insecticides, especially if you want to control Japanese beetles or mosquitoes. Chose those that plants absorb, which requires the insect to feed on the plant to be controlled. Spray when the pests are present and causing problems.

And read the label carefully before you buy the product, before you mix it up and before you spray. Do not mix it any stronger than what the label says.

Plant diseases

Controlling diseases is harder than controlling insects and weeds since most are microscopic. Many weather and growing condition problems can look like fungal diseases.

While most fruit plants are disease magnets, your typical garden plant is bothered more by what you do or don’t do. Too much or too little water or fertilizer, heavy soil, too much mulch, no air movement and poor garden sanitation lead to diseases. You can control most diseases by planting properly.

Roses, tomatoes, fruit trees and turfgrass will always be prone to diseases, though disease resistance is being bred into the plants. In many cases, the best disease control is to remove the plant. If only a few leaves are infected, remove those leaves.

Walk around the yard daily and look at what’s going on. If you can catch a weed, pest or disease problem in its infancy, it’s easier to control. Be observant and take immediate action. Don’t wait.

David Robson is a specialist with University of Illinois Extension. For more gardening information or for your local extension unit office, go to www.extension.uiuc.edu/mg.

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